1. Field of the Invention
The present invention relates to a work machine used for structure demolition works, waste disposal, scrap handling, road works, construction works, civil engineering works, and so forth.
2. Description of the Related Art
Work machines including a track structure for traveling by use of a power system, a swing structure mounted on the top of the track structure to be swingable, a front work implement of the multijoint type attached to the swing structure to be pivotable in the vertical direction, and actuators each of which drives a corresponding front member constituting the front work implement are well known as work machines used for structure demolition works, waste disposal, scrap handling, road works, construction works, civil engineering works, and so forth. As an example of such a work machine, there is a work machine configured based on a hydraulic excavator and including a boom whose one end is pivotably connected to the swing structure, an arm whose one end is pivotably connected to the tip end of the boom, and an attachment such as a grapple, bucket, breaker or crusher attached to the tip end of the arm so that an intended work can be performed.
This type of work machine performs the work while changing its attitude in various ways with the boom, the arm and the attachment of the front work implement projecting outward from the swing structure. Thus, the work machine can lose balance when the operator performs a forceful operation such as putting an excessive workload on a part of the work machine or conducting a quick motion in a state with an excessive load and the front work implement expanded. Therefore, a variety of overturn prevention technologies have been proposed for this type of work machines.
For example, in a technology disclosed in Japanese Patent No. 2871105, angle sensors are provided on the boom and the arm of the work machine and a detection signal from each angle sensor is inputted to a control unit. The control unit calculates the center of gravity of the entire work machine and support force of each stable supporting point at the grounding surface of the track structure based on the detection signals. Support force values at the stable supporting points based on the result of the calculation are displayed on a display device. A warning is issued when the support force at a rear stable supporting point has decreased below a limit value for securing the work safety.
On the other hand, a work machine for performing the aforementioned demolition work carries out the work by driving the track structure, the swing structure and the front work implement that are massive. Thus, if the operator performs an operation for suddenly stopping the driving of the currently moving track structure, swing structure or front work implement for some reason, strong inertial force acts on the work machine and significantly affects the stability of the work machine. Especially when the operator hastily performs an operation for stopping the driving of the currently moving track structure, swing structure or front work implement in response to a warning of a possibility of the overturn from a warning device installed in the work machine, strong inertial force can be added in an overturn direction and that can adversely increase the possibility of the overturn.
To deal with this kind of problem, WO 2012/169531 discloses a control technology, in which variations in the stability until the work machine reaches the complete stoppage in a case where a control lever has been instantaneously returned from an operation state to a stoppage command state are predicted by using a sudden stoppage model and positional information on movable parts of the track structure and the main body including the front work implement, and operation limitation on drive actuators is performed so that no instability occurs at any time till the stoppage.